Amplifier



Patented Apr. 10, 14951 UNITED STATES PATENT AMPLIFIER ApplicationNovember 3l), 1948, Serial No. 62,746

OFFICE -2 Claims.

Our invention relates to an improved amplier for slowly varying currentsor signals.

It is frequently desirable to amplify slowly varying currents orsignals, such as the signals achieved from a photoelectric cell exposedto light of slowly varying intensity. Mechanisms for this purposehaveheretofore been difiicult and expensive in construction since theyhave either involved D.C. amplifiers with the attendant requirements ofcritically stable tube characteristics and applied voltages, or choppingdevices to convert the D.C. signal to an alter nating wave.

` In accordance with the present invention, the

foregoing problems are covercome and improved operation is secured byproviding a saturable reactor energized by the slowly varying current.This reactor is connected in a bridge circuit energized by alternatingcurrent. The resultant voltage is rectified and fed back to the reactor.

It is therefore a general object of the present invention to provide animproved amplifier suitable for use in amplifying current changingslowly with time.

Another object of the present invention is to provide an improvedamplifier for use with a photo-cell.

Still another object of the present invention is to provide an improvedsensitive amplifier for slowly varying signals that requires no chopperor like device and does not demand tubes having particularly stablecharacteristics or voltage supplies having a high degree of stability.

The novel features which we believe to be characteristic of ourinvention are set forth with particularity in the appended claims. Myinvention itself, both as to its organization and method of operation,can best be understood by reference to the following description takenin connection with the accompanying drawing, in which the single figureshows an illustrative embodiment of the invention.

Referring now to the drawing there is shown generally at IS a saturablereactor having saturating leg Illa, and saturable legs Inband Ic.Saturating windings I2 and I4 are received on leg Ia and saturablewinding I has two like portions one on leg Ib and the other on leg Ic.

The winding I2 receives a signal or time-varying current by reason ofthe series circuit de- Cil 2 ned by unidirectional voltage source I8,photocell 2D and winding l2. Thus the saturating leg Ida carries thecurrent or signal to be amplified.

The photo-cell 2i) may be any one of various types vsuch as, forexample, a gas, vacuum or multiplier tube or a lead sulde cell. It iseX- posed to. illumination of intensity varying slowly with time, thuscausing current flow through winding I 2 varying in like manner withtime.

If desired, a photo-voltaic cell may be used to energize winding l2. Inthis case no battery I 3 is required.

The winding i6 is in circuit relationship with inductor 22 andresistances 24 and 25 to denne a bridge circuit having one set ofopposed terminals 23 and 3G and another set of opposed terminals 32 and34.

Alternating voltage is applied across the opposed bridge terminals 32and 34 by the transformer '3B which is energized by alternating voltagesource 33. l

Output voltage from the bridge is taken across terminals 28 and 35. Forthis purpose the primary winding 38o of transformer 38 is connecteddirectly across these terminals. This transformer has two secondarywindings, 38e and 38o, the former acting as an output winding and thelatter as a feedback winding.

The feedback winding 38o is connected to the input set of opposedterminals 4ta and 45D of bridge rectifier 4o. The output set of opposedterminals lilo and dtd is connected through variable resistance 42 tothe saturating winding I4. Thus the winding i4 is energized in responseto the voltage induced in winding 38e.

The rectifier 49 and winding I4 are poled to cause winding I4 to act asa negative feedback winding to oppose the action of winding I2. That is,when current flow through winding I2 increases, the unbalance of thebridge and the resultant change in output voltage of rectifier fil),causes current flow through winding I4 in direction to oppose themagnetomotive force or saturating effect of winding i2 giving rise tothat current.

Preferably the bridge constants are chosen to achieve balance when nocurrent flows in winding I2.

If desired, the winding I4 may be poled to aid rather than opposewinding I2. In this Case the sensitivity of the amplifier is increasedbut the stability and speed of response are reduced.

The output winding 38h is connected to the voltage dividing resistors44, 46, and 48, the latter resistance comprising a switch 48a selectablyconnectable to resistances 43h, 48C or 48d. The com-mon connection ofresistors 48 and 46 is connected to the control electrode of electrontube 5D. The opposite end of resistor 48 is connected to the cathode oftu-be 5U through resistors 52 and 54.

Adjustment of resistance 48 varies the scale range of the instrument E0.

Unidirectional cathode-anode space path voltage is applied to theelectron tube 5@ by unidirectional voltage source 56 and resistance 58which are in series circuit relation across this path.

Meter 60 is an alternating current ammeter responsive to the effectivevalue of the alternating current and is connected in series with thecapacitor 62 and resistance 64 between the anode of tube 5E and theresistance 52.

Condenser 62 blocks D.C. current ow through meter 8B. y

It will be observed that source 5S is connected to the junction ofresistors 52 and 54. This provides stabilizing negative feedback foramplifier tube 50 and thus causes the deection of meter 60 to correspondmore exactly with the value of the induced voltage in winding 3819.

' The saturable reactor lil defines an inductance of value determined bythe net magnetomotive force exerted on leg Iiia by the windings i2 andi4. When this magnetom-otive force increases= the legs lb and itcsaturate and inductance of coil i6 is reduced. Current loW in coil I6does not influence windings l2 and I4 because the uX associated withthis coil is confined to legs IUD and Ic and the connecting portions ofthe core I0.

It will be observed that in the mechanism of the present invention wehave provided a simple and reliable device capable of amplifying thevery low power level and very slow current changes in photo-cell 2d toproduce a usable indication on meter 66. rl'his is accomplished in a,highly stable and sensitive manner and, moreover, does not requireeither a D.C. amplier or a chopper.

While we have shown the amplifier of the present invention adapted toactuate meter 60, it will be evident that it may be used for otherpurposes as well. It may, for example, actuate a resetting mechanismoperable to rebalance the bridge or form part of a closed cycle controlsystem operable to maintain a constant illumination on the photoelectriccell 2D. rIhese, and many other uses will be apparent to one skilled inthe art.

While we have shown a specific embodiment of our invention it will, ofcourse, be understood that we do not wish to be limited thereto sincemany modifications and alternative constructions may be made Withoutdeparting from the spirit and scope thereof. We therefore claim by theappended claims to cover all such modifications and alternativeconstructions as fall within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

l. An amplier adapted to respond to a slowly varying current from a lowenergy level source without reacting thereon comprising in combination,a saturable reactor having a saturating leg and a saturable leg, awinding on the saturating leg adapted to carry said current, a windingon the saturable leg, means defining a bridge circuit incorporating saidlast winding, means to apply alternating potential across one set ofopposed terminals of said bridge circuit, an output transformer having aprimary winding and a secondary winding, means connecting the primarywinding across the other set of opposed terminals of the bridge circuit,a rectier connected across the secondary winding, a second winding onthe saturating leg of the saturable reactor, and means connecting theoutput terminals of the rectier to said last winding.

2. An amplifier adapted to respond to a slowly varying current from alow energy level source without reacting thereon comprising incombination, g, saturable reactor having a saturating legr and asaturable leg, a winding on the saturating leg adapted to carry saidcurrent, a winding on the saturable leg, means defining a bridge circuitincorporating said last winding, means to apply alternating potentialacross one set of opposed terminals of the 4bridge circuit, an outputtransformer having a primary winding and a pair of secondary windings,means connecting the primary winding across the other set of opposedterminals of the bridge circuit, a rectier connected across onesecondary winding, a second winding on the saturating leg of thesaturable reactor, means connecting the output terminals of the lastwinding to the rectifier, and means responsive to the alternating E. M.F. in the other secondary winding to indicate the value of said current.

PAUL T. SEMM. ROBERT T. NAKASONE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

